I was reading page 18 of the DMG under One Hour Preparation. The 4th bullet point described a way of adding bits in an adventure to make a player feel more involved:

Consider how each of these definite encounters relates to the particular motivations of your players. If you have one or more players who are left in the lurch by the encounters you have planned, think about elements you can add to the encounter to hook those players in. For example, if the night’s encounters don’t give your actor player a chance to roleplay, find a way to inject some negotiation into the start of an encounter.

Could I alter a premade adventure's encounters (Keep on the Shadowfell is the adventure I'm hoping to start my first adventure if with) to suit the needs of the characters if the players are looking bored? Also, is this the entire point of D&D's DM – to alter a situation for the benefit of the characters?

@LukeBurgin It's your game: you get to make it as awesome as possible! The adventure writers will never look over your shoulder and tell you you're doing it wrong.
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SevenSidedDie♦Dec 4 '12 at 22:04

3

@LukeBurgin ESPECIALLYif it's a premade adventure. In 30 years of GMing (and over 100 premade adventures) I've only had 5 that didn't require modifications in play - 4 of those were TSR Retail Play modules with Pre-Gen characters. The 5th is the opening adventure from WFRP1E's The Enemy Within campaign, and only once did it not require some mods as well.
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aramisDec 5 '12 at 1:33

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What they said. Modules are like boxes of legos. They give you the parts to build a specific thing but no where does it say you can't add/take pieces or completely redesign.
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CatLordDec 5 '12 at 4:45

As someone who has for years used D&D modules for an entirely different game system and game world, you can and should bend, fold, spindle, and mutilate packaged modules to taste.

Change the scenes to better fit the group you play with. Change, add, or remove encounters to better support the play style that they enjoy -- do they want lots of combat, or prefer roleplaying negotiations? As your campaign progresses and PCs gain bonds/relationships with important NPCs replace new NPCs from modules with ones the players have already encountered -- they did a good job last time so the Queen's Councillor calls on them for another mission.

Drop clues into the current adventure that will lead them to the next adventure (even though these were never designed to be linked, and came from different authors and publishers), and conversely if there are things in a module, such as specific loot, that you don't want in your campaign nix it.

The short version: You bought it, it's yours; the designer won't be checking up. :) Do whatever you like to make it better for your group.

The advantage of D&D, and roleplaying games in general, over other interactive media like video games is that you have human-level intelligences deciding what happens next instead of a more-or-less dumb AI system operating in a pre-programmed game engine with pre-made art assets. There are no "invisible walls" that you can't go through, or actions that are impossible just because there isn't programming for it. If you were playing an RPG of Dragon Age*, you could flirt with any NPC, not just the pre-programmed ones; travel to any location you can get to, not just the ones that they put in the game; try any action, not just the ones there are buttons for.

When you have a human GM† running the game reality instead of a computer, you've got all that flexibility – the only limitation is how quickly they can come up with creative answers to unexpected turns of events. In fact, the very defining experience of a DM is that moment where, despite all your preparation, the players go and do something totally unexpected. It happens to all of us, and the skill of GMing is often summed up by how much skill (and practice — it's totally something that gets better with time and practice) you have in responding to these unexpected choices of the players'.

An important feature of roleplaying is ownership. Your group's play experience is entirely your own to enjoy, and your own to make enjoyable. You get out what you put in. What adventures you play, whether they are published or not, will ultimately be unique in the end experience to your group. There's no way to reproduce perfectly what the designers intended, because they never did intend any such thing: every game and every adventure is designed with the awareness that it will never be played the same twice. So take advantage of that flexibility to make your play experience as enjoyable as you can!

* There is, in fact, a Dragon Age: Dark Fantasy Roleplaying game.
† "GM" or "game master" is the generic term for the person's role. Some games have a more specific term, like D&D's "DM" or "dungeon master".

This last point is the one I think you're looking for. If you can afford to buy a copy of The Neverwinter Campain Setting, you'll find various Themes to add to your players to connect them more deeply to the story, and each other.

You are well versed in a particular subject appropriate to a young
noble scion. Perhaps you spent a lot of time in social gatherings, or
you preferred the solitary pursuit of poring over the volumes in your
family’s library.

Even if you can't get the book, you can just make up relationships on your own, or do what I do and ask them these questions: "How do you know the person sitting on your right? How do you happen to come to be here? Write down your deep dark secret and hand it to me."